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Climate of the Past An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/cp-2019-167
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/cp-2019-167
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 16 Jan 2020

Submitted as: research article | 16 Jan 2020

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This preprint is currently under review for the journal CP.

Global mean surface temperature and climate sensitivity of the EECO, PETM and latest Paleocene

Gordon N. Inglis1,2,a, Fran Bragg3, Natalie Burls4, David Evans5, Gavin L. Foster6, Matthew Huber7, Daniel J. Lunt3, Nicholas Siler8, Sebastian Steinig3, Richard Wilkinson9, Eleni Anagnostou10, Margot Cramwinckel11, Christopher J. Hollis12, Richard D. Pancost1, and Jessica E. Tierney13 Gordon N. Inglis et al.
  • 1Organic Geochemistry Unit, School of Chemistry,School of Earth Science, University of Bristol, UK
  • 2Cabot Institutefor the Environment, University of Bristol, UK
  • 3School of Geographical Sciences, University of Bristol, UK
  • 4Department of Atmospheric, Oceanic and Earth Sciences, George Mason University, USA
  • 5Institute of Geosciences, Goethe University Frankfurt, Frankfurt am Main, Germany
  • 6School of Ocean and Earth Science, University of Southampton, UK
  • 7Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, USA
  • 8College of Earth, Ocean and Atmospheric Sciences, Oregon State University, USA
  • 9School of Mathematics and Statistics, University of Sheffield, UK
  • 10GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany
  • 11Departmentof Earth Sciences, Utrecht University, Netherlands
  • 12GNS Science, Lower Hutt, New Zealand
  • 13Department of Geosciences, The University of Arizona, 1040 E 4th St Tucson AZ USA
  • apresent address: School of Ocean and Earth Science, University of Southampton, UK

Abstract. Accurate estimates of past global mean surface temperature (GMST) help to contextualise future climate change and are required to estimate the sensitivity of the climate system to CO2 forcing during the geological record. GMST estimates from the latest Paleocene and early Eocene (~ 57 to 48 million years ago) span a wide range (~ 9 to 23 °C higher than pre-industrial) and prevent an accurate assessment of climate sensitivity during this extreme greenhouse climate interval. Here, we develop a multi-method experimental framework to calculate GMST during three target intervals: 1) the latest Paleocene (~ 57 Ma), 2) the Paleocene-Eocene Thermal Maximum (56 Ma) and 3) the early Eocene Climatic Optimum (EECO; 49.4 to 53.3 Ma). Using six independent methodologies, we find that average GMST estimates during the latest Paleocene and PETM are 11.7 °C (±0.6 °C) and 18.7 °C (±0.8 °C) higher than pre-industrial, respectively. GMST estimates from the EECO are 13.3 °C (±0.5 °C) warmer than pre-industrial and comparable to previous IPCC AR5 estimates (12.7 °C higher than pre-industrial). Leveraging the extremely large "signal" associated with these extreme warm climates, we combine estimates of GMST and CO2 from the latest Paleocene, PETM and EECO to calculate a gross estimate of the average climate sensitivity between the early Paleogene and today. This yields gross climate sensitivity estimates for the latest Paleocene, PETM and EECO which range between 2.8 to 4.8 °C (66 % confidence). These largely fall within the range predicted by the IPCC (1.5 to 4.5 °C per doubling CO2), but appear incompatible with low values (between 1.5 and 2.8 °C per doubling CO2).

Gordon N. Inglis et al.

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Short summary
This paper presents estimates of global mean surface temperatures and climate sensitivity during the early Paleogene (∼ 57–48 Ma). We employ a multi-method experimental approach and show that: i) Global mean surface temperatures were 12 to 19 °C warmer than pre-industrial and ii) Estimates of "bulk" equilibrium climate sensitivity (~ 3 to 5 °C) fall within the range predicted by the IPCC AR5 Report. Together, this work improves our understanding of two key climate metrics during the early Paleogene.
This paper presents estimates of global mean surface temperatures and climate sensitivity during...
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